Hydraulic servomechanism



March 15, 1966 R. G. HOWARD ET AL 3,240,124

HYDRAULIC SERVOMECHANISM 4 Sheets-Sheet 1 Filed June 12, 1963 INVENTORS ROBERT G. HOWARD HOWARD D. KURTZ March 15, R G HOWARD ET A HYDRAULIC SERVOMECHANISM 4 Sheets-Sheet 2 INVENTORS ROBERT G. HOWARD HOWARD D. KURTZ Agent R. G. HOWARD ET AL 3,240,124

HYDRAULIC SERVOMEGHANISM 4 Sheets-Sheet 5 March .15, 1966 Filed June 12, 1963 March 15, 1966 R HOWARD ETAL 3,240,124

HYDRAULIC SERVOMECHANISM 4 Sheets-Sheet 4.

Filed June 12, 1963 WAVE INVENTORS ROBERT G. HOWARD HOWARD D. KURTZ United States Patent 3,240,124 HYDRAULHI SERVOMECHANISM Robert G. Howard, Northridge, and Howard D. Kurtz, Los Angeies, Calif., assignors to Lockheed Aircraft Corporation, Burbank, Caiif.

Filed June 12, 1963, Ser. No. 287,283 9 Claims. (Cl. 911) This invention relates to a hydraulic servomechanism and more particularly to a dual-parallel, hydraulic servomechanism for aircraft which encompasses a completely independent hydraulic system in each half of a single unit in such a manner that failure or malfunction of one of the systems leaves the other system free to operate along with no loss of aircraft control.

Servornechanisms may be used to position aerodynamic control surfaces on conventional aircraft and to position the thrust levers to vary the thrust output of engines on VTOL aircraft. It is known to increase the reliability of such servomechanisms by providing dual-tandem servomechanisms in which modulating pistons and power pistons from two systems are each mounted coaxially, as with two cylinders having a common piston rod. The tandem or coaxial arrangement insures a fixed relationship between the duplicated systems. Although generally satisfactory, such systems do have certain drawbacks.

One drawback resides in the fact that it is diflicult to detect a malfunction in one half of a dual-tandem system.

Another drawback resides in the fact that it is diflicult to provide a satisfactory seal between each half of the system to prevent transfer of hydraulic fluid from one half of the system to the other half, especially when the latter half of the pair has a reduced, hydraulic supply pressure.

Yet another drawback resides in the fact that it is difficult to detect a malfunction in the electrical systems which automatically control the servomechanism.

In view of the foregoing factors and conditions characteristic of servomechanisms having two-system reliability, it is a primary object of the present invention to provide a new and improved servomechanism not subject to the disadvantages enumerated above and having a dualparallel arrangement in which two independent, servo units are built into a single unit.

Another object of the present invention is to provide a redundant servomechanism having two independent modulating pistons which are linked to a coaxial shaft in such a manner that detection of non-uniformity of action between the two pistons is readily ascertainable.

Yet another object of the present invention is to provide means for detecting a malfunction in a dual-parallel servomechanism.

A further object of the present invention is to provide a dual-parallel servomechanism having new and useful means for matching the performance of separate spool valves.

A still further object of the present invention is to provide a Vernier-type adjustment which permits accurate, rigid positioning of inlet ports of a hydraulic servomechanisrn.

Yet another object of the present invention is to provide a redundant servomechanism for aircraft which employs a completely independent hydraulic system in each half of a consolidated unit in such a manner that failure or malfunction of one of the systems permits the other system to operate individually with no loss of aircraft control.

Another object of the present invention is to provide a dual-parallel servomechanism which will remain in automatic operation even though the electrical system controlling the operation of one half of the servomechanism is interrupted.

3,240,124 Patented Mar. 1 5, 1966' Another object of the present invention is to provide a dual-parallel servomechanism for aircraft having means which will signal the pilot of the aircraft to return to manual controls when the electrical system serving either half of the dual servomechanism malfunctions.

According to the present invention, a dual-parallel hydraulic servomechanism is provided in which a single servomechanism unit encompasses two completely independent hydraulic and electrical systems. In case of failure or malfunction of the hydraulic system or the electrical system in one half of the unit, the corresponding system in the other half will operate alone with no loss of aircraft control. From a conventional, manual or electrical input, the dual systems operate as one to provide a single output. Separate modulating pistons, spool valves and power pistons are provided for each independent system. The two modulating pistons are connected by linkage to coaxial shafts which are held in fixed angular relationship by levers attached to a spring cartridge. Whenever hydraulic forces on the two modulating pistons vary to a suflicient degree, due to a malfunction of either the electrical system or the hydraulic system, to overcome the spring force in the cartridge, the spring will either shorten or extend and thus provide a motion to actuate a switch which indicates the asymmetry of the two systems.

A Vernier-type adjustment is provided on one of the spool valves for the exact alignment of the inlet to the separate spool valve cylinders. The adjustment is accomplished by installing a movable outer sleeve on one valve. The sleeve itself includes a threaded portion having threads of a different lead on its inner and outer surface diameters. Rotation of the sleeve moves the inlets to the desired position over the spool valve. The Vernier-type adjustment permits the accurate, rigid positioning of the inlet ports where distances of 0.001 inch are important for proper operation.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective view showing somewhat schematically a dual-parallel servomechanism of the present invention with a sidewall removed to show internal construction;

FIGURE 2 is a partial plan view of the device of FIG- URE 1 cutaway to illustrate interior portions thereof;

FIGURE 3 is a cross-sectional view taken along line 3-3 of FIGURE 2; and

FIGURE 4 is a longitudinal, cross-sectional view taken along line 44 of FIGURE 3 on an enlarged scale.

Referring again to the drawings and more particularly to FIGURE 1, the dual-parallel servomechanism constituting the present invention, generally designated 10, is shown schematically as comprising a housing member 12 having parallel valve banks 14 and 16 which, for purposes of the schematic description, may be considered to be identical. Therefore, only the elements in bank 14 are shown in full.

A power piston 18 is slidably mounted in a piston chamber 20 near the bottom of bank 14 and is anchored at its ends to fixed members 22 so that relative movement be tween the housing member 12 and the power piston 18 is accomplished by having the housing member 12 slide upon the power piston 18. -A spool valve 24 having a slidable internal portion is mounted in a chamber 26 and is positionable to direct hydraulic fluid under pressure from chamber 26 through a first passageway 28 into chamber 20 on one side of piston 18 and through a second passageway 30 into chamber 20 on the opposite side of piston 18:

Hydraulic fluid under pressure is supplied to the spool valve 24 through a fluid inlet port 32, a passageway 34 and a fluid outlet port 35.

A modulating piston 36 is slidably mounted in a chamber 38 and is positionable by hydraulic fluid which may flow to the chamber 38 on one side of piston 36 through a passageway 40 or to the chamber 38 on the other side of piston 36 through a passageway 42, depending upon the position of an electrically actuated transfer valve 44 which controls the flow of hydraulic fluid through a pressurized fluid inlet 46. The transfer valve 44 may be .of any conventional type which automatically directs fluid to the modulating piston 36 when actuated by signals received through electrical leads 48 and 50, which, in turn, are conventionally connected to a gyroscope, not shown.

The modulating piston 36 is linked to one end of a bell crank 52 and the spool valve 24 is linked to the other end of crank 52 which, in turn, is pivotally mounted on one end of a shaft 54. The other end of shaft 54 is rigidly affixed to one end of a bell crank 56 which has its other end rigidly affixed to one end of a shaft 58. The shaft 58 is rotatably mounted in journals 60 and 60a which form rigid connections with the housing member 12. An aircraft control lever or stick 62 is rigidly connected to shaft 58 so that crank 56 can be rotated by pulling lever 62.

The spool valve 24 may be positioned manually with lever 62 or it may be positioned automatically by modulating piston 36.

The stick 62 is also connected to corresponding elements in the bank 16 of housing member 12 through a crank 56a which is rigidly aflixed to the other end of shaft 58 and a shaft 54a which connects crank 56a to a crank 52a. The crank 52a has one end linked to a spool valve 24a and its other end linked to a modulating piston 36a. The spool valve 24a and the modulating piston 36a are slidably mounted in bank 16 in identical manner with the valve 24 and modulating piston 36 and are controlled by a transfer valve 44a.

Under normal operating conditions, both the banks 14 and 16 will receive identical signals from a common source. Assuming that a signal is received through electrical lead 50 which causes transfer valve 44 to direct fluid to chamber 38 through passageway 40 so that the fluid will exert a force on modulating piston 36 causing it to move to the left, as viewed in FIGURE 1. This will pivot bell crank 52 about shaft 54 in a counter-clockwise direction sliding spool valve 24 to the right. As spool valve 24 moves to the right, outlet port 35 is uncovered so that fluid under pressure will flow from passageway 34 through chamber 26 and passageway 28 into chamber 20 where the fluid exerts a force on the right hand side of power piston 18, as viewed in FIGURE 1. Since power piston 18 is anchored, this force will cause housing member 12 to move to the right, as viewed in FIGURE 1. Since bell crank 52 is connected to housing member 12 through shaft 54, bell crank 56 and shaft 58, movement of housing 12 while stick 62 remains stationary will close outlet port 35 shutting off the flow of fluid to power cylinder 18. The elements mounted in bank 16 will operate in an identical manner.

A pair of bell cranks 64 and 64: each have one end rigidly aflixed to shafts 66 and 66a, respectively, which are rotatably mounted in journals 68 and 68a forming a rigid connection with housing member 12. The other ends of bell cranks 64 and 64a are linked to the modulating pistons 36 and 36a through links 69 and 69a, respectively, so that linear motion of pistons 36 and 36a results in an angular motion of shafts 66 and 66a. Bell cranks 70 and 70a are rigidly aflixed to the shafts 66 and 66a, respectively, and each has a pair of legs 72 and 74 mounted at right angles to each other. Each leg 72 is connected by links 75 to a transducer 76 which convert the angular motion of shafts 66 and 66a into signals which are sent back to the transfer valves 44 and 44a, respectively, as feedback signals. The feedback signals tend to move the transfer valves in a direction that would tend to balance the respective modulating pistons to a central position. The arms 74 are linked together by means of a differential spring cartridge 78 having a microswitch 80. The spring 82 of the differential spring cartridge 78 is designed in such a manner that, should either of the modulating pistons 36 or 36a become depressurized, the spring 82 will cause the depressurized piston to follow exactly the movement of the pressurized piston. If, on the other hand, either system should malfunction so that the modulating pistons are not synchronized with one another, the bias of spring 82 is overcome tripping the microswitch and cuts off the current to the solenoids 86 and 86a. A conventional spring (not shown) returns the solenoid and the respective transfer valve back to a de-energized position. A conventional signalling circuit (not shown) is coupled to the microswitch 80 and it concurrently signals the aircraft pilot to discontinue the automatic operation of servomechanism 10 by de-energizing solenoids in each bank, such as the solenoid 86 for bank 14. This opens a by-pass valve in each bank, such as the by-pass valve 88 in bank 14, so that the modulating pistons 36 and 36a will be depressurized. The modulating pistons 36 and 36a will then be returned to neutral positions by a centering spring cartridge 90 which has one end anchored to a fixed member 92 and its other end connected to one of the arms 74. The spring 94 in cartridge 90 is firm enough to maintain the modulating pistons 36 and 36a in a static condition so that the end of hell cranks 52 and 52a which are linked to the pistons 36 and 36a, respectively, become fixed fulcrum points.

Under these conditions, if an input force is applied to stick 62, moving it to the right, as viewed in FIGURE 1, bell cranks 56 and 56a will rotate clockwise, swinging bell cranks 52 and 52a in a clockwise direction. This causes spool valves 24 and 24a to move to the right. This movement of spool valves 24 and 24a uncovers their respective ports, such as the port 35 for valve 24. Uncovering of port 35 permits fluid under pressure to flow through line 28 into chamber 20 on the right side of power cylinder 18 causing housing member 12 to move to the right, all as viewed in FIGURE 1, covering port 35.

It is apparent that the system in bank 14 and the system in bank 16 and their linkage mechanism must be exactly synchronized for satisfactory operation of the servomechanism 10. It is also apparent that conventional manufacturing tolerances will not permit the various systems to be exactly synchronized upon assembling the mechanism 10. Therefore, as will appear hereinafter, one of the spool valves is provided with a Vernier-type adjustment so that the system in one bank may be adjusted to operate identically with the system in the other bank.

Referring now to FIGURES 2-4, the parts which have been shown schematically in FIGURE 1 are shown in detail in bank 16 and will now be described by using the same reference numerals to refer to the parts generally.

The piston assembly 18a is mounted in a chamber 20a and includes a piston and a piston rod 102 having its end connected to fixed members 22a. The piston 100 is provided with a piston ring 104, a right hand piston face 106 and a left hand piston face 108. A hearing 110 is mounted on rod 102 at each end of the chamber 20a, each bearing being maintained in position by means of retainers 111 having external threads 112 engaging internal threads 114 at the ends of chamber 20a. The bearings and retainers are conventionally sealed by O-rings and packing glands to prevent leakage of hydraulic fluid.

The spool valve 24a, most specifically illustrated in FIGURE 4, has conventional four-way porting and includes an encompassing sleeve 124 in which is provided a pressure port 125 communicating with port 35a in bank 16, a first power-cylinder port 126 communicating with passageway 3011, a second power-cylinder port 127 communicating with passageway 28a, and a fluid-return port 128 communicating with a sump 130 mounted in housing 12. A plurality of resilient seals 132 are employed to seal the various ports from one another and to seal the sleeve 124 in chamber 26a. A cylindrical insert 134 is mounted in the sleeve 124 with one end abutting a retainer ring 136. It is maintained in position by a threaded insert 137 having external threads 138 which engage internal threads 139 on sleeve 124. A pressure port 144), relief ports 142 and power-cylinder ports 144 are provided in insert 134 leading into a series of annuli adjacent the respective ports in sleeve 124. Flow of hydraulic fluid through the power-cylinder ports 144 is controlled by a piston assembly 146 which is slidably mounted in insert 134. The piston assembly 146 includes lands 148, controlling flow of fluid through power-cylinder ports 144, lapped balance grooves 150 and a passageway 152. The passageway 152 extends through the piston 146 and communicates with the sump 130. The piston assembly 146 also includes a collar 154 which is normally biased into engagement with a perforated plate 156 by a compression spring 158 having one end bearing against an end cap 160 and its other end bearing against a nut 162 which threadedly engages one end of piston assembly 146. A fluid damper 164, having an orifice 166, is secured adjacent the perforated plate 156 by a perforated nut-plate 168 which threadedly engages the piston assembly 146 and is restrained against rotation by means of a friction plug 170.

The cap 160 has an external thread 172 which has a first, predetermined lead and which threadedly engages the internal thread 174 in chamber 26a. The cap 160 also has an internal thread 176 which has a second predetermined lead ditfering from the lead of the thread 172 and which threadedly engages an external thread 178 on sleeve 124. A wrench-engaging surface 180 is provided on cap 160 so that a wrench may be employed to thread the valve 24a into chamber 26a. A dowel pin 182 may be inserted in an opening 184 in housing 12 to engage a slot 186 formed on sleeve 124, thereby preventing rotation of the valve 24a while permitting the sleeve 124 to slide longitudinally within chamber 26a when cap 160 is subsequently rotated. Since the thread 172 has a first lead and the thread 176 has a second, diiferent lead, the sleeve 124 and the cylindrical insert 134 carried by the sleeve 124 may be very finely adjusted relative to the lands 148 on piston assembly 146. This is an important feature of the invention because it permits adjustment of the hydraulic system in bank 16 to exactly synchronize with the system in bank 14. A friction plug 188 is mounted in sleeve 124 and engages the internal thread 176 on cap 160 restraining cap 160 against unwanted rotation by vibrational forces.

The modulating piston 36a is mounted in a chamber 38a and includes a piston 180 and a piston rod 192. The iston 190 includes a ring groove 198 in which a piston ring 199 is mounted. The link 69b connects one end 280 of piston rod 192 to the upper end of bell crank 52a. A first conventionally sealed bushing 206 threadedly engages one end of chamber 38a. A second similarly sealed bushing 214 is maintained in position at the other end of chamber 38:: by a retainer 216 which encompasses the end of the piston rod 192 and is abutted by an end cap 218. The end cap 218 threadedly engages housing 12 and is sealed thereto with an O-ring.

Passageways 46a and 42a connect a pressure-fluid inlet port 46a in valve 44a with chamber 38a adjacent opposite sides of piston 190. A solenoid 86a, a by-pass valve 88a, and leads 48a and 50a are also provided.

The servomechanism may be connected to an aircraft control, not shown, by means of a bearing 220 threadedly engaging housing 12 and which is prevented from rotating by a lock nut 224.

Caps 226 and 226a are employed to cover sumps 130 and 130a, respectively and seals 228 and 228a are mounted in the caps 226 and 226a, respectively, to form a wiping connection with links 69a and 69, respectively.

While the particular dual-parallel servomechanism herein shown and described in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiment of the invention and that no limitations are intended to the details of construction or design herein shown other than as defined in the appended claims.

What is claimed is:

1. A hydraulic servomechanism comprising:

a housing having a first and second power pistons and a first and second spool valves mounted therein,

a first and second passage means connecting the first and second spool valves to the first and second power pistons respectively, the spool valves controlling flow of hydraulic fluid to the power pistons,

a port means mounted in the housing for connecting the spool valves to a source of hydraulic fluid under pressure,

an input means mounted on the housing for positioning the spool valves simultaneously to direct hydraulic fluid under pressure to the power pistons through the passage means,

the input means including:

(a) first and second modulating pistons slidably mounted in said housing;

(b) third and fourth passage means mounted in said housing for connecting said first and second modulating pistons, respectively, to a source of hydraulic fluid under pressure;

(c) first and second valve means mounted in said housing for controlling the flow of fluid through said third and fourth passage means, respectively, in response to electrical input signals; and

(d) first and second linkage means connecting said first and second modulating pistons to said first and second spool valves, respectively.

2. The servomechanism of claim 1 wherein said input means comprises:

(a) a manual input lever pivotally mounted on said housing;

(b) first and second modulating pistons slidably mounted in said housing;

(c) third and fourth passage means mounted in said housing for placing said first and second modulating pistons, respectively, into communication with a source of hydraulic fluid under pressure;

((1) first and second valve means mounted in said housing for controlling flow of hydraulic fluid to said first and second modulating pistons, respectively, in response to input command signals; and

(e) first and second linkage means connecting said manual control lever to said first and second spool valves and to said first and second modulating pistons, respectively.

3. The servomechanism of claim 2 including third and fourth linkage means connecting said first and second modulating pistons, respectively, to feedback means for feeding a signal back to said first and sec-ond valve means.

4. The servomechanism of claim 3 including:

(a) differential spring cartridge means connecting said third and fourth linkage means together in such a manner that a predetermined force acting upon one of said modulating pistons is transmitted through said third and fourth linkage means and said differential spring cartridge to the other of said modulating pistons; and

(b) sensing means connected to said differential spring cartridge means for sensing a predetermined, unequal force transmitted by said modulating pistons through said third and fourth linkage means.

5. The servomechanism of claim 4 including a centering spring cartridge connected to said third and fourth linkage means for returning said modulating pistons to a predetermined neutral position when they are not being acted upon by a hydraulic force.

6. The servomechanism of claim wherein one of said spool valves contains a Vernier-type adjustment means permitting said one spool valve to be synchronized for identical parallel performance with the other said spool valve.

7. In a dual-parallel servomechanism having modulating pistons adapted to operate in unison in response to command signals, means for detecting non-unison operation of said modulating pistons comprising:

(a) first linkage means connected to one of said modulating pistons and second linkage means connected to the other said modulating pistons;

(b) differential spring cartridge means connecting said first and second linkage means together, said differential spring cartridge means including a compression spring adapted to change its length upon nonunison operation of said modulating pistons; and

(c) sensing means connected to said spring for emitting a signal when said spring changes its length.

8. A hydraulic servomechanism comprising:

(a) a housing having first and second power pistons and first and second spool valves mounted therein;

(b) first and second passage means connecting said first and second spool valves to said first and second power pistons, respectively, said spool valves controlling flow of hydraulic fluid to said power pistons;

(c) a manual input lever mounted on said housing for positioning said spool valves simultaneously to direct hydraulic fluid under pressure to said power pistons through said passage means;

(d) first link means connecting said lever to said spool valves, first port means mounted in said housing for connecting said spool valves to a source of hydraulic fluid under pressure;

(e) means anchoring said power pistons whereby said housing slides on said power pistons when said hydraulic fluid is directed thereto through said passage means;

(f) first and second modulating pistons slidably mounted in said housing;

(g) third and fourth passage means mounted in said housing for connecting said first and second modulating pistons, respectively, to a source of hydraulic fluid under pressure;

(h) first and second electrical valve means mounted in said housing for controlling the flow of hydraulic fluid through said third and fourth passageways, respectively, in response to electrical input signals;

(i) third and fourth link means connecting said first and second modulating pistons to said first and second spool valves, respectively;

(j) fourth and fifth link means connecting said first and second modulating pistons, respectively, to electrical feedback means for feeding an electrical signal back to said first and second electrical valve means;

(k) differential spring cartridge means connecting said fourth and fifth link means together in such a manner that a predetermined force acting upon one of said modulating pistons will be transmitted through said fourth and fi-fth link means and said differential spring cartridge to the other of said modulating pistons;

(l) sensing means connected to said differential spring cartridge means for sensing a predetermined, unequal force transmitted by said modulating pistons through said fourth and fifth link means; and

(m) a centering spring cartridge connected to said fourth and fifth link means for returning said modulating pistons to a predetermined neutral position when they are not being acted upon by a hydraulic force.

9. The servomechanism of claim 8 wherein one of said spool valves contains a Vernier-type adjustment means permitting said one spool valve to be synchronized for identical parallel performance with the other spool valve.

References Cited by the Examiner UNITED STATES PATENTS 2,597,419 5/1952 Westbury et al 91216 2,773,660 12/1956 Rasmussen 91216 2,826,896 3/1958 Glaze et a1. 91216 2,920,650 1/1960 Moog 137625.69 2,942,583 6/1960 Rue 137625.69 2,943,606 7/1960 Willis et a1. 91216 3,015,313 1/1962 Faisander 91-365 3,098,412 7/1963 Reitman 9l-216 SAMUEL LEVINE, Primary Examiner.

FRED E. ENGELTHALER, Examiner. 

1. A HYDRAULIC SERVOMECHANISM COMPRISING: A HOUSING HAVING A FIRST AND SECOND POWER PISTONS AND A FIRST AND SECOND SPOOL VALVES MOUNTED THEREIN, A FIRST AND SECOND PASSAGE MEANS CONNECTING THE FIRST AND SECOND SPOOL VALVES TO THE FIRST AND SECOND POWER PISTONS RESPECTIVELY, THE SPOOL VALVES CONTROLLING FLOW OF HYDRAULIC FLUID TO THE POWER PISTONS, A PORT MEANS MOUNTED IN THE HOUSING FOR CONNECTING THE SPOOL VALVES TO A SOURCE OF HYDRAULIC FLUID UNDER PRESSURE, AN INPUT MEANS MOUNTED ON THE HOUSING FOR POSITIONING THE SPOOL VALVES SIMULTANEOUSLY TO DIRECT HYDRAULIC FLUID UNDER PRESSURE TO THE POWER PISTONS THROUGH THE PASSAGE MEANS, THE INPUT MEANS INCLUDING: (A) FIRST AND SECOND MODULATING PISTONS SLIDABLY MOUNTED IN SAID HOUSING; (B) THIRD AND FOURTH PASSAGE MEANS MOUNTED IN SAID HOUSING FOR CONNECTING SAID FIRST AND SECOND MODULATING PISTONS, RESPECTIVELY, TO A SOURCE OF HYDRAULIC FLUID UNDER PRESSURE; (C) FIRST AND SECOND VALVE MEANS MOUNTED IN SAID HOUSING FOR CONTROLLING THE FLOW OF FLUID THROUGH SAID THIRD AND FOURTH PASSAGE MEANS, RESPECTIVELY, IN RESPONSE TO ELECTRICAL INPUT SIGNALS; AND (D) FIRST AND SECOND LINKAGE MEANS CONNECTING SAID FIRST AND SECOND MODULATING PISTONS TO SAID FIRST AND SECOND SPOOL VALVES, RESPECTIVELY. 